Communication system



June 13, 1939. v R H CAMPBELL 2,162,371

COMMUNICATION SYSTEM Filed oct. 29, 1937 c J L 105 g l 105 E Patentedy J une 13, 1939 COMMUNICATION SYSTEM Richard H. Campbell, Racine,- Wis., assigner to Webster Electric Company, Racine, Wis., a corporation oi Wisconsin Application October 29, 1937,-Serial No. 171,627 Z3 Claims. (Cl. 179-1) This invention relates to communication systems and particularly to telephonie communication systems in which suitable voice receiving and.'l

transmitting means, such as dynamic loud speak- 5- ers of the type comprising a permanent magnet.

are employed for the dual function of receiving and transmitting, the fluctuations in electrical current created in the transmitter being amplied by suitable amplifying means.

According to the presentl invention there are provided a plurality of stations located remote from each other. a loud speak-er unitand several of the stations y are provided with ampliers and selector switches operable to connect the station with which they are associated to any one of the remaining stations. These stations are also provided withselectively operable plural position master switches for connecting the speaker unit at the station to 20 the input or output of the associated ampliner,

or through one of lthe aforementioned selector switches to the other stations.

` Each station has associated therewith an interstation conductor with which the selector switch is normally in engagement and to which the loud 25 speakers that do y not have amplifiers control switches associated therewith are permanently connected.

The master switchesare so constructed and arranged in circuit with the loud speakers, amplifiers and interstation conductors that communication can be maintained between any stations provided .with like apparatus or a loud speaker alone by simple manipulations of master switches. The latter normally, i. e., when the system is not vnuse and the amplifier is inoperative, occupy a first position in which the speaker unit associated with any particular master switch is connected to an interstation conductor through the selector switch so that any one of the several stations provided with an amplifier may communicate therewith even though the amplier at the station be-V ing called is deenergized. The master switches are operable into second position in which the 45 speaker unit is connected to the output of its own amplifier and the interstation conductor is connected to the input of the amplier. In this position of the master switches any of the other stations may communicate with the station even though these other stations are not provided with amplifiers. The master switches are also operable into a third position permitting the operator at. that station to communicate withfany of the remaining stations. In this position the speaker unit at the associated station is con- Each station is provided with nected to the input andthe interstation conductor is connected to the output of the'amplifler.

A primary object of the present invention is to provide an -intercommunicating system in which a number of different types of apparatus maybe joined together and operated with a minimum of efiort and likelihood of confusion.

A further object is so to construct the communication controlling masterswitches that they are biased to return to a predetermined -position from one or more of the other positions to simplify operation `of the system and prevent the operator at any' station from leaving the apparatus at his station in suchcondition that the station cannot be called.

`A further object of the invention is to provide a master switch adapted to control not only the communication circuits but also the supply of power to the amplier.

Ay further object is to provide an intercommunicating system comprising apparatus of the type described in which a minimum of interstation conductors are used and according to which independent conversations can be carried on between two stations or several stations can be connected together for conference purposes.

Other advantages and objectsof the present invention will become apparent from the ensuing description in the course of which reference is had to the accompanying drawing, in which,

Figure l is va schematic diagram of one embodiment of the present invention; and

Figure 2 is a schematic circuit diagram of a modified form of the invention.

Referring rst to Figure l, the reference numeral 9 designates voice receiving and transmitting means such, as a dynamic loud speaker of the type employing a permanent magnet and a voice coil suspended in the field thereof, located at a station indicated by the reference numeral I. Similar loud speaker units I0 and II areprovided at stations 2 and 3 located remote from stationv I and from each other.

Stations I and 2 are provided with identical apparatus including amplifiersl2 and I3, respec- 45 tively, so that operators thereat may initiate communication with other stations, be they provided with similar apparatus or simply a loud speaker unit, as station 3. The apparatus at stations I and 2 includes three position master 50 switches I4 and I5, respectively,- for enabling the operators thereat to control the energization of the amplifiers, the direction of communication and tocondition the stations for the reception of speech from any station provided with an ampliconductor er of its own. Stations I and 2 are provided also with selector switches I6 and I1 for selectively connecting the stations to other stations included in the system.

While the apparatus in each of stations I and 2 is identical, it is believed that the indication of the various parts thereof by separate reference numerals will add tol the clarity of the description. For this reason, the apparatus at station I is described in detail rst and the apparatus in station 2 described briefly thereafter.

The amplifier I2 at station I is provided with the usual input and output transformer coils |8 and I9, each of which has one terminal thereof connected to a common conductor 2| which is grounded as indicated at 2| 'Ihe other terminals of the input and output coils are connected by conductors 22 and 23 to interconnected contacts 24 and 25 and inter-connected contacts 26 and 21, respectively, of the master switch. The remaining contacts 28 and 29 of the master switch are connected together by a conductor 3|.

The master switch I4 is provided with a pair of communication circuit controlling switch blades 32 and 33 mechanically inter-connected for simultaneous operation by the operator at station I, and is spring biased from its lowermost or third to its middle or second position. Blade 33 is connected by a conductor 34 to one terminal of the voice coil 35 associated with speaker unit 9, the other terminal of which is connected by a conductor 36 to the common conductor 2 I. Blade 32 is connected to the selector switch I6 by a 31 connected to the switch blade 38 comprising a part of the selector switch.

The master switch I4 also comprises a switch blade 39 controlling the energization of the amplier and mechanically inter-connected to blades 32 and 33. The blade is adapted to engage an elongated contact 40 in certain hereinafter described positions of the master switch to supply the amplifier with a suitable B potential and thereby render it operative. The amplifier filaments (not shown) are continuously supplied with power from a suitable source (also not shown) so that as soon as the B supply is connected to the ampliiier the latter is immediately ready to perform its usual function.

'I'he selector switch blade 38 is adapted to establish a circuit from the conductor 31 to any one of a plurality of inter-station conductors 4|, 42, 43, and 44. 'I'hese inter-station conductors extend to all of the stations forming the communication system.

The apparatus at station 2 is, as stated previously, identical with that atstation I. Thus the ungrounded ends of input and output coils and 46 of the amplier I3 are connected by conductors," and 48 to the master switch I5. Conductor 41 is connected to the inter-connected contacts 5| and 52 of the master switch and conductor 48 is connected to the interconnected contacts 53 and-54. Contacts 55 land 56 of the master switch are interconnected by a conductor 51. The switch blades 58, 59 and 50 are mechanically interconnected for simultaneous operation and are spring biased from their lowermost to middle positions. Switch blade 59 is connected by a conductor 6I to the voice coil 62 associatedwith speaker unit Ill, the other terminal of which is connected by a conductor 63 to the common conductor 2|, which extends to station 2 as well as to the remaining stations. Switch blade 53. is connected by a conductor .64 to the selector switch blade 65. Switch blade controls the B supply for the amplifier and has associated therewith a contact 60' engaged thereby when the switch is actuated to predetermined pbsitions. Switch blade corresponds to switch blade 38 and like the latter may be selectively actuated to establish a circuit from conductor 64 to any one of the interstation conductors 4I to 44, inelusive.

In addition to the similar stations I and 2 described above, the system may comprise one or more secondary stations having no amplier or control means and, therefore, with no means for initiating or controlling the direction of communication. Station 3 is of the latter type and the voice coil 66 associated with the speaker unit II thereat is connected by a conductor 61 to interstation conductor 43. The other terminal of voice coil66 is connected by a conductor 68 to the common conductor 2| which extends also to station 3. 4

In the preferred mode of operation it is contemplated that the selector switch associated with any particular station is connected to the interstation conductor corresponding to that station. In the present instance station I has associated therewith the interstation conductor 4I and station 2 has associated therewith the interstation conductor 42. Therefore, switch blade 38 normally establishes a circuit from conductor 31 to conductor 4| and switch blade 65 establishes a circuit from conductor 64 to conductor 42.

According to this arrangement the system is so arranged that any station may be called from any otherr station, provided, of course. that the station from which it is desired to initiate conversation is provided with amplifier. For instance, station 2 may be placed in communication with station I simply by actuation off-the selector 'switch 65 into engagement with conductor 4I,

as illustrated by the dotted lines in Figure 1,v and thereby placing the direction of communication under control of the master switches.

The master switches' I4 and I5 at each station are usually left in the positions indicated so that the interstation conductor associated with that station is connected directly to the voice coil of the speaker unit at that station and the amplifier B supply cut 01T. The interstation conductor `4| thus is connected to voicey coil 35 of speaker unit 9 through a circuit that is as follows: Switch blade 38 in engagement with conductor 4|, conductor 31, switch blade 32 in engagement with contact 28, conductor 3|, switch blade 33 in engagement with contact 29 and conductor 34. The return circuit from the voice coil extends through conductor 36 and the common conductor 2|. the position lindicated by the dotted lines, either the input or output of amplifier I3 may be connected to speaker unit 9 through operation of the master switch I5. When the master switch is actuated into its lowermost position, switch blade 58 engages contact 53 and the switch blade 59 engages contact 52, thereby connecting voice coil 62 to the input coll of amplifier I3 through conductor'II, switch blade 59 in engagement with contact 52, and conductor 41.l The circuit to the input coil is completed in obvious fashion through Y conductor 63 and the common conductor 2|.

The output coil 46 of amplifier I3 is simultaneously connected to the interstation conductor 4| through a .circuit including conductor 48,

,switchfblade- 58 in engagement with contact 53,

and conductor 64 leading to the interstation conductor 4| through the switch blade 55 in its dotted 'l Il Thus, when switch blade B5 is actuated into line position. Thus, the operator at station 2 may communicate with the operator at station I.

At thistime the system may be operated in4 Ation to establish a circuit from contacts I and 54 to the switch blades 58 and 59, thereby connecting the speaker unit 3 to the input of the amplifier I3 and the speaker unit I Il across the output of amplifier I3. The voice coil of speaker unit 9 is connected to the `input through the interstation conductor 4I, switch 55 in engagement therewith, conductor 64, switch blade 53 in engagement with contact 5I, and conductor 41 leading to the input coil. The return circuit to' lihood of confusion veven thoughdiierent types of apparatus be installed at the several stations.

vthe voice coil is completed through the common conductor `2I and conducor 33. Speaker unit I3 is connected across the output coil I46 througha circuit including conductor 43, switch blade 59 in engagement with contact 54, and conductor 6I leading to voice coil 62, the return circuit being completed through conductor 63 and the cornmon` conductor 2I. Under this mode of operation station 2 is a master station and Aonly the master switch I5 is actuated to reverse the direction of communication. This mode of operation may be carried on by the operator at station I who can manipulate master switch I4 in a similar manner.

However,if the operator at the `station 2 did not desire to use amplifier I3 during reception, and actuated the master switch I5, to its uppermost position, the operator at station I is able tocommunicate with the operator at station 2 simply by operating the master switch I4 at station I to its lowermost position. This operation results in the connection of lspeaker unit 9 to the input of amplifier AI2 through conductor 34, switch blade 33 in engagement with contact 25, and conductor 22. The output of |ampliiler I2 is simultaneously connected to the interstation conductor 4I through a circuit including conductor 23, switch blade 32 in engagement `with contact 26, and conductor 31. Since the speaker unit III is connected to the interstation conductor when the master switch I5 is in its uppermost position, the output of amplier I2 is connected thereto. To reverse the direction of communication, it is necessary to reverse the positions of the master switches.I

After completion of a conversation, the operators at both stations usually return the master switches to their uppermost positions, thereby cutting off the B supply to theaniplier and connecting the speaker unit to the interstation conductor to condition the station for receiving calls. I n case an operator fails to r-do this, operators at the remaining stationscan call because in all events the master switch is returned to its intermediate position in which the station is conf dtioned to receive messages through its own amplifier.

In the event an oprator at station I or 2, or

any similar station, desires to communicate with the secondary station 3, he may ldo so by manipulating the selector switch into engagement with the interstation conductorconnected with station 3. Thus, if the operator at 'station I desires to communicate with the operator atstation 3, he simply manipulates switch blade 33 to ,establish a-circuit from conductor 31 to interstation conductor 43. Then, upon operation ot the master switch I4 into the talk position, in which switch blade 32 is in engagement with contact 26 and switch blade 33 is in engagement with contact 25, the output of amplier I2` is impressed across the voice coil Biot speaker unit II. When the operator at station I desires to listen to the operator at station 3 he operates the master switch I4 into its intermediate position, thereby connecting voice coil 66 across the input of the amplifier and voice'coil 35 of the speaker unit 3 across the output.

The last describedl mode of operation is similar to the first of the two alternative modes of operation when communication is hadbetween stations |I and 2, according to which station 2 was operated as a master station; It is seen, therefore, that the system as a ywhole 'can be operated in a uniform'and simple manner with little like- Furthermore, `continuity of operation Ais assured even though some of the amplifiers may become inoperative for any reason, such as defective tubes or the like.

The system described labove possesses the advantage that it can be used for conferences and the .like between a plurality ci stations. ever it is desired to hold a conference between operators at three or more `stations alloperators actuate their selector switches into engagement with a particular interstation conductor. Whenever a particular operator wishes Yto speak, he simply actuates his master `switch into its lowermost or talk position, the remaining operators allowing their master switches to remain in the upper position. At such time the amplifier unit at the station from which the operator is talking is the one utilized, as described above.

Furthermore, a plurality of independent conversations can be carried on over the system without interference.. For example, communication can be established between stations I and 3 simjply by operation of selector switch blade 38 at station I to close a circuit to interstation conductor 43. Simulaneously, communicatoin can be established between station 2 and a station associated with interstation conductor 44 (not shown, but which may correspond to stations I and 2 or 3) by operation of selector switch blade Whenat station 2 to close a circuit to conductor 43.

In the modiiication of the invention illustrated in Figure 2 the construction of the master switch has been modied in such manneithat its normal position is the intermediate one in which the loud speaker unit associated therewith is con` nected to the interstation conductor and from which it is actuated into the upper position to listen through its own ampliilerand into its lower position for transmitting through its ownl amplifier. The embodiment of-Figure 2 also utilizes a diiere'nt type of interstation conductor, each interstation conductor comprising a pair of conductors, one-conductor of each pair being connected to similar conductors oi every other pair to `form theA common conductor 2| oi the prevlously described modification.

As in the previously described modication, a plurality oi.' stations I,` 2, and 3 are illustrated. Loud speaker units 3. I0, and II are located at these three stations, respectively,` and station I has associated therewith a continuously energized amplifier 12, and station therewith a similar amplifier 13. These two stations are also provided with master switches 14 1 has associated and 15 and selector switches 16 and 11, respectively. Master switches 14 and 15 have been shown as comprising three and two communication circuit controlling blades respectively to 5- illustrate somewhat different switch constructions.

Amplifier 12 has its input and output coils 18 and 19 connected by conductors 8| and 82 to switch blade 83 and stationary contact. 84,-and to switch blade 85, respectively, of the master switch 14. The latter comprises three switch blades including a third one 86, which along with blades 83 and 85 are all operable into three positions. 'Ihe switch blades are normally biased 15 into the intermediate position illustrated by suitable spring means. Switch blade 83 has associated therewith three stationary contacts 86, 81, and88, of which contacts 81 and 88 are no't included in any circuit; switch blade 86 has associated therewith three stationary contacts 89, 9|, and the previously mentioned contact 84; and switch blade 85 has associated therewith three contacts 92, 93, and 94. As illustrated in Figure 2, switch blades 83, 85, and 86 are normally in engagement with contacts 81, 93, and 9|, respectively. Contacts 89 and 92 are inter-connected by a conductor 95 and the three contacts 86, 9| and 94 are joined by conductors 96 and 91. The three last mentioned contacts are also connected by a conductox` 98 to the selector switch 99. Switch blade 86 is connected by a conductor |8| to the voice coil 35 o1' speaker unit 9, the opposite terminal of which and one terminal of input and output coils 18 and 19 are all connected to a common conductor 2|. Thelatter has'an extension to conductors |82, |83, |84, and |85, each forming a single conductor of a group of twisted pairs provided for the purpose of decreasing hum and other objectionable noise originating in the interstation conductors. The other conductors of each pair, including conductors |86, |81, |88, and |89, are provided with branch conductors to H4, 1nclusive, leading to the selector switch 16 at station I.

Before proceeding with the description of master switch 15, it may be noted that interstation conductors |86 to |89 are connected by branch conductors ||5 to ||8, respectively, to the selector switch 11. The latter is connected by conductor 2| to the master switch.

Themaster switch 15 diifers from switch 14 only in construction. It. consists of two blades |22 and |23 connected by conductors |24 and |2| to voice coil 62 and selector switch 11. Each blade is operable into three positions and is biased into its intermediate position. Contacts |25 to |21 associated with blade |22 are connected to contacts |3I to |33 by conductors |34 to |36.' Contacts |21 and 13|, which are interconnectedby conductor |36, are connected to the input of the `amplifier by conductor |31 and contacts v|25 and |33, which are interconnected by `conductor |34, are connected to the output by c nductor |38. Theswitch blades |22 and |23 are lmechanically interconnected and biased into engagement with contacts |26 and |32, thereby normally connecting loudspeaker unit to selector switclr11.

The' embodiment of Figure 2 may'also be provided with a .number of stations 3 comprising simply a loud speaker unit. In the present in-l stant the loudspeaker 3 has its associated voice coil 66 connected by conductors |4| and |42 across' conductors |84 and |88.

i ,"'mitting station.

Under normal conditions the selector switches 16 and 11 are in positions connecting voice coils 35 and 62 to interstatlon conductors |86 and |81, which are, therefore, the interstation conductors for stations and 2, respectively. -This connection extends through master switches 14 and 15 in their normal intermediate positions.

In the normal positions of the master switches one station can communicate with another simply by operation of its associated selector switch into engagement with the interstatlon conductor associated with the latter and operation of'the master switch thereat to its lowermost, or talk, position.

When the operator at station desires to communicate with the operator at station 2, he actuates selector switch blade 99 to establish a circuit from conductor 98 to conductor ||2, thereby connecting conductor 98 to the interstatlon conductor |81 associated with station 2. Inasmuch as the selector switch 11 is in engagevment with conductor ||6, the result is the connection of the speaker unit |8 to conductor 98. 'I'he operator at station thereafter depresses switch 14 into its lowermost position thereby connecting conductor 98 to the output coil 19 of amplifler 12 and the speaker unit 9 across the input coil 18 of the amplifier. The circuit to the input coil 18 extends from voice coil 35 through conductor |8I, switch blade 86 in engagement with contact 84, and conductor 8|. The connection of output kcoll 19 to the speaker unit |8 extends through conductor 82, switch blade 85 in engagement with conductor 94, conductors 96 and 98, switch blade 99 in engagement with conductor ||2, interstation conductor |81, and conductor H6, selector switch 11, and switch blades |22 and |23.

Alter the operator at station l calls the operator at station 2, the described system may be operated according to two methods. The iirst corresponds to the first of the two methods previously described according to which the master switch 14 at station alone is used to control thc direction of communication. For transmitting, it is actuated to its lowermost position as above indicated and for'receiving, it is actuated to its uppermost position in which the interstatlon conductor (and speaker unit I8) are connected -to the input of amplifier 12 and the speaker unit 9 is connected to the output of the amplifier. It

imay be seen, therefore, that the apparatus at the calling station alone isused, although it should be noted that the called station can be given control over the direction of communication.

According to the second method, both ampli- `iers are used, the amplier used at any particular time being the one associated with the trans- When operating according to this method, the master switches are depressed from their normal middle positions to their lowermost positions when transmitting and released to condition the station for reception.

Whenever any one of the operators desires to communicate with the operator at station 3, he may do so Just as inthe previously ldescribed modification. Likewise, a conference between the y the art that any number o1' stations may be added.

For instance, there may be as many stations as there are interstation conductors or several stations may be connected to a single conductor. The addition of other stations entails merely an 5 increase in number of interstation conductors and a corresponding change in the selector switch so that the latter may close a circuit to all conductors.

What I claim as new and wish to secure by United States Letters Patent is:

1. In an intercommunication system, the combination including a plurality of stations remote from each other, voice receiving and transmitting means and an amplifier having input and output connections at each station, interstation conductors between stations, and means at each station for controlling the connections of said voice receiving and transmitting means and interstation conductors to said amplier and to each other,

y said means being operable into a first position in which the interstation conductor is connected to said voice receiving and transmitting means, to a second positionin which the interstation conductor and voice receiving and transmitting means are connected to the input and output, respectively, of the ampliiier, and to a third position in which the connections of the voice receiving and transmitting means and interstation conductor to the ampliiier are reversed.

2. In an intercommunication system, the combination including a plurality of stations remote from each other, voice receiving and transmitting means and an amplifier having input and output connections at each station, interstation u; conductors between stations, means at each station for controlling the connections of said' voice `receiving and transmitting means and interstation conductors to said amplifier and to each other, said means being operable into a rst position in which the interstation conductor is connected to said voice receiving and transmitting means, to a second position in which the interstation conductor and voice receiving and transmitting means are connected to the input and output, respectively, of the amplifier, and to a `third position in which the connections of the voice receiving and transmitting means and interstation conductor to the ampliiier are reversed,

and biasing means for returning said control means from said third mentioned position to said second mentioned position.

3. In an intercommunication system, the combination including a plurality of stations remote from each other, voice receiving and transmitting means and an amplifier having input and output connections at each station, interstation conductors between stations, means at each station for controlling the connections of said voice receiviiig and transmitting means and'interstation conductors to said amplier and to each other,

said means being operable into a rst position in which the interstation conductor is connected to said voice receiving and transmitting means, to a second position in which the interstation conductor and voice receiving and transmitting means are4 connected to the input and output, respectively, of the amplifier, and to a third position in which the connetcions of the voice receiving and transmitting means and interstation conductor to the amplifier are reversed, and biasing means for returning lsaid control means from said second and third mentioned positions to said first mentioned position. l

4. An intercommunication system, including in 75 combination, a plurality of stations remote from each other, voice receiving and transmitting means and an amplifier having input and output connections at each station, interstation conductors between stations, and means including a plural position switch and a selector switch at each station for normally connecting the voice receiving and transmitting means thereat to an interstation conductor, said plural position switch being operable into two displaced positions, in the iirst of which the interstation conductor and receiving and transmitting means are connected to the input and output of said ampliiier, respectively, and in the second of which the interstation conductor and the receiving and transmitting means are connected to the output and input oi' said amplier.

5. In an intercommunication system, the combination including a plurality of stations remote from'each other, voice receiving and transmitting means and an amplier having input and output connections at each station, a source of power supply for said amplifier, interstation conductors between stations, and a plural position switch for controlling the connections of said voice receiving and transmitting means and interstation conductors to said amplifier and to each other, said switch being operable into a rst position in which the interstation conductor is connected to said voice receiving and transmitting means, to a second position in which the interstation conductor and voice receiving andtransmitting means are connected to the input and woutput, respectively, of the' amplifier. and to a third position in which the connections of the voice receiving and transmitting means and interstation conductor to the amplifier are reversed, said switch including also means for cutting ofi the supply of power to the amplifier when operated into said first-mentioned position.

6. An intercommunication system, including, in combination, a plurality of stations remote from each other, receiving and transmitting means and an amplier having input and output connections at each station, interstation con-` ductors between stations, and means including a three position master switch and a selector switch for controlling the connection of the receiving and transmitting means and the interstation conductors to the ampliiier, said selector switch being operable to condition the receiving means and amplifier for connection to any interstation conductor, and said master switch being biased to a position to complete the connection of the receiving and transmitting means directly to the interstation conductor and operable between two other positions to reverse receiving and transmitting means and the interstation conductor to the input and output of the. ampliiier.

7 An intercommunication system, including in combination, a pair of stations remote from each other joined by an interstation conductor, voice receiving and transmitting means at each station, an ampliiier at each station, switch at each-station normally biased to a position in which the voice receiving and transmitting means at each station is connected to the interstation conductor, and circui s adapted selectively to be completed 'by said switch in its other positions for connecting the voice receiving and transmitting means to the input or output of the amplifier and' simultaneously connecting the interstation conductor to the output or input of the .amplien the connections of the i a plural position4 8. An intercommunication system. including, in

combination, a plurality of stations remote from each other, an interstation conductor associated with each station, a loud speaker unit, an amplifier having input and output connections, a twopole three-position switch, a connection from the loud speaker unit to one blade of said switch, a connection from the other blade to an interstation conductor, said blades being operable into l engagement with a first pair of interconnected with each station, a loud contacts whereby the interstation conductor is connected to the unit for reception of communication from another station provided with an amplifier, a connection from the output of the amplifier to a second pair of interconnected contacts, one of which `is adapted to be engaged by the first switch blade in its second position, and the other by the second switch blade in its third position whereby the interstation conductor is connected to the input and the loud speaker unit to the'output of the amplifier forE the reception of signals from a station without an amplifier, a connection from the input of the amplifier to a third pair of interconnected contacts, one of which is adapted to be engaged by the first switch blade in its third position, and the second switch blade in its second position whereby a speaker unit is connected to the input andthe interstation conductor to the output of the amplifier, for the transmission of signals to other stations, and said switch being provided with resilient means for returning the blades from said third-mentioned position to said second-mentioned position, and being so constructed that the blades remain in said first-mentioned position when operated thereinto.

9. An intercommunication system, including, in combination, a plurality of stations remote from each other, an interstation conductor associated y speaker unit and amplifier having input and output connections, a two-pole three-position switch, a connection from the 'loud speaker unit to one blade of said switch, ia connection from the other blade to an inter- 4station conductor, said blades being normally biased into engagement with a first pair of interconnected stationary contacts whereby the interl Vstation conductor is connected to the speaker unit `for reception of signals from another station provided 'with an amplifier,.'a connection from the output of the amplifier to a second pair of interconnected contacts, rone of which is adapted to be engaged by the first switch 'blade in its second position and the other by the second switch bladey inits third position whereby the interstation conductor is connected to the input and the loud speaker unit to the output of the amplifier for the reception of signals from a station without an amplifier, and a connection from the input of the amplifier to a third pair of interconnected contacts, one of which is adapted to be engaged by the first switch blade in its third position and the second switch blade in its second position,

whereby the speaker unit is connected to the input and the interstation conductor to the output of' the amplifier for the transmission of signals to other stations.

10. An intercommunication system, including, in combination, a plurality of stations remote from each' other,'an interstation conductor associated with each station and a conductor common to all stations, a loud speaker unit and amplifier having input and output connections at each station, a connection from the loud speaker unit and amplifier input and output to the common conductor, a three-pole, three-position switch, a connection from the input of the ampliiier to one switch blade, a connection from the loud speaker to the second blade, a connection from the output of the amplifier to the third blade, said switch being biased into an intermediate position in which the second blade engages a contact connected to an interstation conductor and the other blades are in open circuit position, whereby the station is conditioned for reception of speech from any station provided with an amplifier, said switch being operable to a first displaced position in which the first blade engages a contact connected to the interstation conductor and the remaining blades engage a pair of interconnected contacts, whereby the station is conditioned for reception of speech from other stations, and' said switch being operable to a third position in which the first blade is in open circuit position, the second blade engages a contact connected to the input of the ampiiiier, and the third blade engages a contact connected to the interstation conductor, whereby the station is conditioned for the transmission of signals to other stations.

11. An intercommunication system, including in combination, a plurality of stations, an equal number of individual interstation conductors and a common conductor, voice receiving and transmitting means an'd an amplifier at each station, a selector switch at each station for establishing a circuit therefrom to any of said interstation conductors, and means including a plural position master switch at each station for reversing the connection of the voice receiving and transmitting meansthereat and interstation conductor to the input and output ot the amplifier.

12. An intercommunication system, including in combination, a plurality of stations, an equal number of individual interstation conductors and a common conductor, voice receiving and transmitting meansand an ampliiierat each station, a selector switch at each station, and means including a plural position master switch at each station for connecting the voice receiving and transmitting means thereat to an associated interstation conductor through said selector switch,

said master switch being operable to two other'O to the output and in the otherof which these connections are reversed, and said selector switchbeing operable to establish a circuit to any of said interstation conductors, whereby communication can be established between two or more stations by operation ofthe selector switches thereat to establish a circuit to a predetermined interstation conductor.

13. An intercommunication system, including in combination, a plurality of stations, an equal number of individual interstation conductors and a common conductor, voice receiving and transmitting means and an amplifier at each station, a selector switch at each station, and means including a plural position master switch at each station for connecting the voice receiving and transmitting means thereat to an associated interstation conductor through said selector switch, said master switch being operable to two other positions, in one of which the interstation conductor is connected to the input of the amplifier and the voice receiving and transmitting means to the output, and in the other of'which these connections are reversed, and said selector switch being operable to establish a circuit to any of said interstation conductors, lwhereby, a plurality of independent communication circuits can be established between groups of two or more stations by operation of selector switches in each group to establish circuits to predetermined interstation conductors.

14. An vintercornmunication system, including in combination, a plurality of stations, voice receiving and transmitting means and an amplifier at each station, communication circuits between stations, and means at each station for controlling the -connection of the communication circuit to that station and the voice receiving and transmitting means thereat to the amplier, said control means normally occupying a position in which the communication circuit is established through the voice receiving and transmitting means and operable to two displaced positions in a first of which the voice receiving and transmitting means is connected to the input of the amplifier and the communication circuit to the output, and in the second of which the connections of the voice receiving and transmitting means and communication circuit to the amplifier are reversed.

15. In an intercommunicating system, the combination including an amplifier, having input` and output connections, a `source of power for said amplifier, voice receiving and transmitting means, and a plural position switch for controlling the connections of said voice receiving and transmitting means and said amplifier, said switch being operable into a first position to connect said voice receiving and transmitting means to the input of lsaid amplifier, to a second position to connect the voice receiving and transmitting means to the output of said amplier, and to a third position to disconnect said voice receiving and transmitting means from said amplier and simultaneously cut oi! the supply of power to the amplier.

16. In an intercommunicating system, the combination including an amplifier, having input and output connections, a source of power for said amplifier, voice receiving and transmit- 'ting means associated therewith, and single switch means for simultaneously controlling the supply of power to said'amplier and the connections of the voice receiving and transmitting means to the input and output of the amplifier.

17. In an intercommunicating system, the combination including a plurality of stations, certain of said stations being provided with voice receiv-v ing and transmittingmeans and amplifiers, and others of said stations being provided with voice receiving and transmitting means only, interstation conductors leading to all'stations, and communication control switches so constructed and arranged in circuit with the voice receiving and transmitting means, amplifiers, and interstation conductors that stations provided with switches may be placed in communicating relationship with other similar stations through either the amplifier at that station or said similar station, andwith the remaining stations throughthe amplier at that station.

18. In an intercommunicating system, the combination including a plurality of stations, certain of -said stations being provided with voice receiving and transmitting means and amplifiers, and others` of said stations being provided with voice receiving and transmitting means only, interstamunication control switches so constructed and arranged in circuit with the voice receiving and transmitting means, amplifiers, and interstation conductors that communication may be maintained between other similar stations' according to two modes of manipulation of said switches, and with the remaining stations, according to one of said modes of manipulation.

19. A unit adapted to be connected in an intercommunioating system of the loudspeaking type, including in combination, voice receiving and transmitting means adapted to function as a microphone and loudspeaker, an amplifier having input andoutput connections, a conductor adapted to be connected to other units in the system, and -means associated with said voice receiving and transmitting means, amplifier and conductor for controlling the connections thereof, said means being operable into a first position to connect said voice receiving and transmitting means to said conductor and to a second position to connect said conductor to the input 'and said voice receiving and transmitting means tothe output of said amplifier.

20. A unit adapted to be connected in an interccmmunicating system of the loudspeaking type, including in combination, voice receiving and transmitting means adapted to function as a microphone and loudspeaker, an amplifier having input and output connections, a conductor adapted to be connected to other units in the system, and means associated with said voice receiving and transmitting means, amplifier and conductor for controlling the connections thereof, said means being operable into a first position to connect said voice receiving and transmitting means to said conductor, to a second position to connect said conductor to the input and and transmitting means adapted to function as the connections of the voice receiving and transmitting means and the conductor to the amplifier are' reversed, said last-mentioned means belng adapted also to de-energze-said amplifier when in said first mentioned position.

22. A unit for use at a station in an intercommunicating system of the loudspeaker type, including in combination, an amplifier, a source of "potential for said amplifier, voice receiving and loudspeaker, an amplifier havl and transmitting means of the type adapted to function as a microphone and loudspeaker, a conductor adapted to be connected to other stations in the system, and switch means adaptedto control the connections of said amplifier, conductor, and voice receiving and transmitting means whereby communication can be carried on between said station and other stations, said switch cluding in combination, an amplier, a source of power for said amplifier. a voice reproducer, an interstation conductor, and single switch means for simultaneously connecting said reproducer to said interstation conductor and disconnecting 5 seid ampliner from said source of power.

RICHARD H. CALIPBELL. 

